UNITED STATES ENVIRONMENTAL PROTECTION AGENCY

NATIONAL VEHICLE AND FUEL EMISSIONS LABORATORY

2565 PLYMOUTH ROAD

ANN ARBOR, MICHIGAN 48105-2498

 OFFICE OF

AIR AND RADIATION

March 30, 2012

CD-12-07 (Revised) 

(LDV/LDT/MDPV/HDV/ICI/LD-AFC)

SUBJECT: Assigned Deterioration Factors

Dear Manufacturer:

This letter provides revised EPA assigned deterioration factors (ADFs) for determining 

compliance with certain chassis-based exhaust and evaporative emission standards. These 

revised ADFs apply to vehicles that must meet a Tier 2 or heavy-duty chassis-based exhaust 

emission standard, and also to vehicles which must meet a Federal LEV-II or heavy-duty 

evaporative emission standard. The revised ADFs are presented in Tables 1 and 2, which are 

attached to this letter. The ADFs presented in this guidance letter supersede the ADFs in EPA 

guidance letter CCD-05-10 for Tier 2 vehicles and are effective immediately.

Applicability

The additive exhaust emission ADFs in Table 1 supersede the multiplicative ADFs in EPA 

guidance letter CCD-05-10 dated May 26, 2005. The new ADFs must be used by original 

equipment manufacturers (OEMs) electing to use EPA ADFs for demonstrating compliance 

under Tier 2 or heavy-duty chassis exhaust emission standards. The revised 

evaporative/refueling additive ADFs must be used by OEMs electing to use EPA ADFs for 

demonstrating compliance under Federal LEV II, or heavy-duty evaporative emission standards. 

Usage of ADFs is contingent on OEMs qualifying under the small volume manufacture and 

small volume test group provisions of 40 CFR § 86.1826-01 as provided in 40 CFR paragraphs 

86.1838-01(b)(1) and 86.1838-01(b)(2). 

Qualifying small volume alternative fuel converters and Independent Commercial Importers 

(ICIs) also use ADFs to demonstrate compliance with exhaust and evaporative emission 

standards. Fuel converters modify previously certified OEM products and demonstrate 

compliance with emission standards under EPA regulations in 40 CFR Part 85 subpart F. ICIs 

bring previously uncertified vehicles into compliance with applicable EPA standards. Thus both 

alternative fuel converters and ICIs that have need for ADFs must now follow the new guidance 

provided in this letter. 

Given that only recent model year (MY) OEM deterioration factors (DFs) were analyzed using 

EPA’s Verify data system (data from 2009 and later MYs for analysis of Tier 2 and heavy-duty 

exhaust emission data, and data from 2010 and later MYs for analysis of the evaporative 

emission data) the ADFs in Tables 1 and 2 apply to only certain MYs of vehicles that must 
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comply with emission standards under fuel conversion or ICI regulations. For example, it is not 

appropriate to use the ADFs in Tables 1 and 2 for determining compliance under earlier 

standards, such as NLEV or Tier 1 emission standards. Therefore, effective with the issuance of 

this guidance letter, Tables 1 and 2 apply to fuel conversions of OEM 2004 model year (MY) 

and later chassis tested vehicles certified under Tier 2 standards, and also to fuel conversions of 

OEM 2005 MY and later chassis certified heavy-duty vehicles. Evaporative emissions ADFs 

presented in Table 2 apply to fuel conversions of OEM 2009 MY and later light-duty vehicles 

and heavy-duty chassis certified vehicles. Similar limitations as a function of MY apply to the 

use of ADFs for ICI vehicles.

Fuel converters and ICIs requesting the use of an EPA ADF outside the MY ranges described 

above will need to contact EPA. EPA will assign these types of DFs on a case-by-case basis. 

 

Authority

EPA is issuing these new ADFs under the regulatory authority in 40 CFR §86.1826-01, in 

particular the authority for the Agency to assign deterioration factors, and to periodically update 

and publish these in a guidance document or advisory circular, provided in paragraph 40 CFR 

§86.1826-01(b).

Methodology

A recent assessment of the ADFs contained in EPA guidance letter CCD-05-10 suggests that the 

use of multiplicative ADFs may no longer be appropriate since the original equipment 

manufacturers (OEMs) primarily have used additive DFs since the beginning of emission 

compliance under Tier 2 standards.

The ADFs in Tables 1 and 2 are based on an analysis that ranks OEM additive ADFs from 

lowest to highest, and then finds the 70th percentile value, as contemplated under 40 CFR 

§86.1826(b)(1)(i). In order to overcome the problem of insufficient gasoline OEM DFs for Tier 

2 bins 2, 6, and 7, it was determined reasonable to combine bins 2 and 3, combine bins 4 and 5, 

and combine bins 6, 7, and 8. EPA vehicle certification regulations are structured such that the 

DFs associated with a durability group may be used across a number of test groups. Prior to 

finding the 70th percentile values, data were filtered for a given combination of useful life and 

manufacturer durability group to eliminate duplicate DFs for the newly combined bins 2-3, 4-5, 

and 6-8. A similar approach was followed for analysis of additive evaporative ADFs, but 

understanding that there are no evaporative emission durability groups, only evaporative 

emission families. Standards for evaporative emission are developed as a function of vehicle 

class, where each class corresponds to a unique evaporative emission standard. Thus, the ADFs 

provided in Table 2 are also shown as a function of vehicle class.

The OEM data used for developing the new ADFs are derived from the EPA Verify data base. 

Records for MYs 2009-2012 were used for analysis of OEM exhaust emission DFs. Records for 

MYs 2010-2012 were used in the derivation of evaporative emission ADFs. These MY ranges 

were selected to correspond to final phase-in of the Tier 2 and heavy-duty exhaust emission 

standards and final phase-in of the LEV-II and heavy-duty evaporative emission standards.
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Analyzing OEM additive DFs provides a more robust sample size compared to the number of 

OEM multiplicative DFs. Nevertheless, the analysis of additive DFs revealed inadequate data 

samples for alternative fuels. There are very few (none in some cases) additive OEM DFs for 

vehicles certified on CNG, LNG, LPG, and diesel fuel, and few OEM DFs for vehicles certified 

to the ethanol bin standards. Based on knowledge of exhaust temperature development data at 

the catalyst inlet, it is reasonable to conclude that, in general, OEM DFs developed on gasoline 

would represent a worst case DF relative to DFs developed using CNG, LNG, LPG, and ethanol 

fuel types. Therefore, OEMs, fuel converters, and ICIs wishing to use ADFs on vehicles that 

will use alternative fuels, may use the gasoline ADFs presented in Tables 1 and 2. There are also 

inadequate numbers of OEM DFs for chassis certified heavy-duty vehicles. Given that chassis 

certified heavy-duty vehicles are sometimes certified to MDPV bin 8 standards, EPA concludes

it is reasonable to use bin 6-8 exhaust ADFs for demonstrating compliance with heavy-duty 

standards. 

OEMs, fuel converters, and ICIs that desire to use an EPA ADF for new fuel types and advanced 

vehicle and emissions control technologies must contact EPA for guidance.

EPA contact

For further questions on this guidance letter contact Martin Reineman at by email at 

reineman.martin@epa.gov.

Sincerely,

Byron J. Bunker, Acting Director

Compliance Division

Office of Transportation and Air Quality

Enclosures
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Enclosure 1 to CD-12-07

Table 1 - Tier 2 Gasoline Exhaust Emission Additive ADFs [1][2][3][4][5]

Tier 2 Bins Useful Life NMOG g/mi CO g/mi NOx g/mi HCHO mg/mi

2-3 120K 0.0020 0.12 0.002 0.0

5 50K 0.0049 0.11 0.005 0.1

4-5 120K 0.0123 0.29 0.014 0.3

6-8 50K 0.0118 0.24 0.016 0.2

6-8 [6] 120K 0.0299 0.61 0.040 0.4

[1] For fuel converters and ICIs, these ADFs are applicable to 2004 model year and later 

vehicles chassis certified under Tier 2 or heavy-duty exhaust emission standards. See EPA if 

ADFs are needed for earlier model year vehicles. The previous multiplicative ADFs in guidance 

letter CCD-05-10 may still be appropriate for older vehicles needing to meet standards under 

pre-Tier 2 compliance programs.

[2] To convert a 120K ADF to an optional 150K ADF, use the following equation:

150K ADF = (120K ADF)(146K/116K)

[3] Table 1 ADFs are also applicable to gasoline hybrid, ethanol FFVs, CNG, LNG, and LPG 

vehicles

[4] Not enough PM data were available for development of an assigned DF. Compliance 

statements may be used in lieu of PM measurement

[5] Table 1 not applicable to diesels – see EPA if necessary

[6] Bin 6-8 ADFs may be applied to heavy-duty chassis test results
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Enclosure 2 to CD-12-07

Table 2 - Federal LEV II, HDV Gasoline Evaporative Emission

120K Additive ADFs [1][2][3][4][5]

Evaporative/Refueling Test Vehicle Class Additive DF

2 Day Diurnal + Hot Soak Light-Duty Vehicles 0.010 g

2 Day Diurnal + Hot Soak Light Light-Duty Trucks 0.007 g

2 Day Diurnal + Hot Soak Heavy Light-Duty Trucks 0.010 g

2 Day Diurnal + Hot Soak Medium-Duty Passenger Vehicles 0.000 g

2 Day Diurnal + Hot Soak Heavy-Duty Vehicles 8500 – 14,000 

GVW

0.000 g

3 Day Diurnal + Hot Soak Light-Duty Vehicles 0.013 g

3 Day Diurnal + Hot Soak Light Light-Duty Trucks 0.000 g

3 Day Diurnal + Hot Soak Heavy Light-Duty Trucks 0.000 g

3 Day Diurnal + Hot Soak Medium-Duty Passenger Vehicles 0.000 g

3 Day Diurnal + Hot Soak Heavy-Duty Vehicles 8500 – 14,000 

GVW

0.000 g

Running Loss [6] All Classes 0.000 g/mi

ORVR [7] All Classes 0.005 g/gal

[1] For fuel converters and ICIs, ADFs are applicable to 2009 model year and later light-duty 

and heavy-duty chassis certified vehicles. The previous additive evaporative emission ADFs in 

guidance letter CCD-05-10 may still be appropriate for older vehicles needing to meet standards 

under pre-Tier 2 compliance programs.

[2] To convert a 120K ADF to an optional 150K ADF, use the following equation:

150K ADF = (120K ADF)(146K/116K)

[3] Evaporative emission test waivers may apply in lieu of testing closed gaseous fuel systems

[4] Evaporative emission/refueling standards do not apply to diesel fueled vehicles

[5] No 2-day standards for dedicated CNG, LNG, or dedicated LPG vehicles

[6] No running loss standards for dedicated CNG, LNG, or dedicated LPG vehicles

[7] No ORVR standards for dedicated CNG or LNG vehicles but industry standard practice 

must be followed for design of fuel fill receptacles.